The present invention relates to a system for monitoring the operation of input circuits to a central control and monitoring unit for machines and/or devices usable in production and/or product packaging lines, for example production lines for making cigarettes and/or for packaging packets of cigarettes. Such lines can, for example, include cigarette-making machines, filter fitting machines, packaging machines, cellophane wrapping machines, carton-making machines or parcel-forming machines.
As is known, such individual machines or production lines are controlled by a central control and monitoring unit which, in dependence on determined signals emitted by input transducers, determines the appropriate operating instants of the various output transducers, which can also belong to different machines in the same line. Such a central control and command unit receives input signals from input transducers by means of respective input circuits.
These input transducers can include switching devices (for example microswitches or proximity sensors), devices which provide signals at relatively high frequency, of the order of several tens of kHz, (for example signals coming from synchronization systems), and devices which provide alternating voltage signals having a frequency of the order of several tens of Hz (for example signals coming from transformers).
Further, such central control and monitoring units also detect the action of the control at the output transducers, by means of associated monitoring circuits which are coupled to the central unit by means of respective input circuits.